x³-x²+x²-13x+12=0
x²(x-1)+(x-12)(x-1)=0
(x-1)(x²+x-12)=0
(x-1)(x+4)(x-3)=0
x=1,x=-4,x=3x²(x-1)+(x-12)(x-1)=0(x-1)(x²+x-12)=0不太明白从第一步怎么到第二步？提取公因数x-1